This invention relates generally to radiation systems and methods and in particular to methods and apparatus for imaging patients' breasts with high resolution to identify cancerous lesions with microcalcifications.
Breast cancer is one of the most common cancers among women in the United States. Each year, about 200,000 American women are diagnosed to have breast cancer. One of eight women born today will be diagnosed with breast cancer at some time during their lifetime. For successful treatment of breast cancer, early detection and diagnosis are crucial. Conventional X-ray mammography has been shown a cost-effective tool for early detection of breast cancer. However, the predictive value and specificity of X-ray mammography are limited partly due to projecting a three-dimensional breast into a two-dimensional image. The minimum cancerous lesion size that can be detected by conventional X-ray mammography has been on the order of 10 mm in diameter, which is about 1000 times larger than a 1 mm cancerous lesion in volume. It is believed that a 1 mm cancerous lesion grows at an exponential growth rate that finally leads to a lesion with 10 mm size when the growth rate begins to decrease. It would be desirable to detect and monitor the growth of cancerous lesions at early stages.
FIG. 1 shows a conventional computed tomography (CT) machine for imaging patients' breasts. The machine includes a single C-arm with an X-ray imager attached at one side and an X-ray tube mounted at the opposite. In use the patient lies prone with a pendulant single breast to be imaged protruding through a hole in the support couch. The C-arm supporting the X-ray imager and X-ray tube rotates to provide cone beam CT image data sets or limited angle digital tomosynthesis data sets. The CT machine shown in FIG. 1 allows the breast tissue to be imaged without the need to flatten or compress the breast as in mammography. Confusion caused by superposition of soft tissue layers as in mammography may be avoided as the soft tissue layers can be decomposed into desired single cross-sectional image slices without the interference of features in layers before or after the particular image slice. However, the CT machine shown in FIG. 1 does not provide the spatial resolution to resolve microcalcifications, tiny calcium deposits inside the breast tissue which pattern has high correlation with cancer. Microcalcifications are used to diagnose about 50 percent of breast cancers and are found to accompany about 80 percent of actual breast cancers.